Throughout this application various publications are referred to within parentheses or by footnote. The contents of these publications are hereby incorporated by reference in their entirety.
Introduction
The physiological reaction in a mammal to the interaction of IgE antibodies present in said mammal upon contact with the corresponding antigen is generally referred to as allergy. It is believed that the allergic response evolved to combat infections with parasites. As parasitic infections are rare in industrialized countries this mechanism becomes pathologic in certain susceptible (atopic) individuals. Characteristic of allergies is that the antigen, also called the allergen, is normally innocuous, and the body's reaction is inappropriate.
Allergic reactions can involve all body tissues but are most prominent in the boundaries with the external environment: the airway, eye, gastrointestinal tract and skin. The conditions are known as allergic rhinitis in the nose (hay fever), allergic asthma in the lungs, food allergies in the GI tract and allergic hypersensitivity (hives) or dermatitis in the skin. Anaphylaxis refers to the systemic reaction that occurs when an allergen is introduced directly into the circulation, such as occurs with injection of drugs and insect stings. A massive early phase reaction occurs throughout the body. Symptoms include diffuse airway swelling and hypotension which can be life threatening.
Each year more than 50 million Americans suffer from allergic diseases, costing the health care system $18 billion annually (American Academy of Allergy, Asthma and Immunology (AAAAI). The Allergy Report: Science Based Findings on the Diagnosis & Treatment of Allergic Disorders, 1996-2001)
Alarmingly, the prevalence and severity of allergic disorders has rapidly increased in the United States over the past twenty years, so there is a need for new therapies for these conditions.
In 1998, an estimated 15 million Americans, or 6.4 percent of the population, had asthma, with 5 million being children. Children account for 4.8 million of Americans with asthma. Each year, 1.8 million emergency room visits are for asthma, nearly 500,000 Americans are hospitalized and more than 5,000 die from the disease. Although asthma deaths are infrequent, they have increased significantly during the last two decades. From 1975-1979, the death rate was 8.2 per 100,000 people. That rate jumped in 1993-1995 to 17.9 per 100,000. Asthma cost the U.S. economy an estimated $10.7 billion in 1994, including a direct health care cost of $6.1 billion and indirect costs, such as lost workdays, of $4.6 billion.
Approximately 16.7 million office visits to health care providers each year are attributed to allergic rhinitis alone (CDC. Fast Stats A-Z, Vital and Health Statistics, Series 10, no. 13, 1999
A related condition, chronic sinusitis, is the most commonly reported chronic disease, affecting 12.6 percent of people (approximately 38 million) in the United States in 1996. Another related condition, serous otitis media, is the most common condition in children requiring an office visit to a health care provider.
Atopic dermatitis is one of the most common skin diseases, particularly in infants and children. The estimated prevalence in the United States is 9 percent Rudikoff D and Lebwohl M. “Atopic dermatitis.” Lancet 351(9117): 1715-21. 1998
Experts estimate that food allergy occurs in 8 percent of children 6 years of age or under, and in 1 to 2 percent of adults Sampson H A. In Allergy, Principles and Practice, 5th Ed., E. Middleton et al, ed. Mosby, St. Louis, p. 1162. 1998.
Pathophysiology of Allergy
Allergy is an ailment that affects millions of individuals worldwide. Attempts to desensitize an individual against a material that causes an allergic response (hereafter designated as an “allergen”) by injection of measured dosages of the allergen heretofore has failed to achieve complete relief of allergy symptoms reproducibly in all allergic individuals. An allergic response is a term of art and has a well-defined meaning. Within the context of the present invention, an allergic or reagenic response includes, in particular, at least one of the features of 1.) production of an abnormally high level of IgE in an individual's serum, 2.) immunologic interaction between an allergen, an individual's IgE and leukocytes resulting in release of histamines, 3.) production of hives, rashes, wheal and flare and similar dermatological manifestation of hypersensitivity, and 4.) anaphylaxis.
An allergic response is a state of hypersensitivity in which an exaggerated immune response is induced by the exposure to a particular antigen or allergen. Hypersensitivity reactions can be classified as immediate or delayed. Immediate or type I hypersensitivity (or anaphylactic response) is an allergic reaction which develops very quickly, i.e., within seconds or minutes of exposure of the patient to the causative allergen, and it is mediated by IgE antibodies produced by B lymphocytes. In non-allergic patients, there is no IgE antibody of clinical relevance. However, in a person suffering with allergic diseases, IgE antibody mediates immediate hypersensitivity by sensitizing mast cells which are abundant in the skin, membranes of the eye, nose and mouth, and in the respiratory tract and intestines.
IgE secreted from activated B cells can attach to Fc receptors located on the surface of mast cells and basophil granulocytes, which contain numerous cytoplasmic granules packed with chemical mediators e.g. histamine (J. Klein, “Immunology”, Blackwell Sci. Pub., London, 1990; E. Benjamini & S. Leskowitz, “Immunology”, Wiley-Liss, N.Y. 1991). This receptor binds circulating IgE with very high affinity and retains it at the mast cell surface for extended periods of time. Activation is accomplished through the binding of an allergen simultaneously to more than one polyvalent molecule of Fc receptor-bound IgE. This “cross linking” of at least two surface-bound IgE molecules brings Fc receptor proteins into close association with one another in the plane of the mast cell plasma membrane. When the bound IgE is contacted by the appropriate allergen, the mast cell becomes activated. Kinases associated with these receptors become activated as a result of this proximity. They initiate the second messenger cascade, which results in the fusion of the granules with the cell surface membrane, leading to the exocytosis of the granule contents, such as histamine, cytokines, and leukotrienes into the surrounding tissue, and the concomitant induction of allergic symptoms. It is the activity of these substances which is responsible for the clinical symptoms typical of immediate hypersensitivity. These include contraction of smooth muscle in the airways or the intestine, the dilation of small blood vessels and the increase in their permeability to water and plasma proteins, the secretion of thick sticky mucus, and in the skin, swelling and the stimulation of nerve endings that results in itching.
Delayed type hypersensitivity (DTH) reactions are mediated by T-cells and macrophages become evident only after 1 to 2 days and persist from several days to a few weeks. DTH is also referred to as cell-mediated hypersensitivity (i.e., T-cell mediated) and is part of a larger group of reactions called cell-mediated immunity.
Anaphylaxis, or anaphylactic shock, is an acute systemic (whole body) type of allergic reaction, it occurs when a person has become sensitized to a certain substance or allergen (that is, the immune system has been abnormally triggered to recognize that allergen as a threat to the body). On the second or subsequent exposure to the substance, an allergic reaction occurs. This reaction is sudden, severe, and involves the whole body. Anaphylaxis is life-threatening and can occur at any time.
Therapeutically, many agents are used to try to prevent the release of mediators from mast cells and basophils and/or to treat the downstream events by blocking or ameliorating the effects of the mediators on target tissues. Therapeutic agents commonly employed fall under the following main groups.
Antihistamines block and mop up the released histamine, i.e. the major mediator of the allergic response.
Alpha-1 beta-2 agonists, e.g., Epinephrine, Salbutamol overcome indirectly the downstream effects on vasculature and smooth muscle.
Chromoglycate is useful for primary prevention of mast cells/basophil degranulation. This prophylactic must be taken continuously. It does not prevent the cross-linking of IgE but it somehow interferes with subsequent events. Theophylline and other phosphodiesterase inhibitors again influence downstream biochemical events particularly associated with cyclic nucleotides. Steroids have multiple sites of activities against the allergic response. They are either administered locally and/or systemically.
None of the above treatments are ideal for the modulation of allergic responses because each has specific problems such as side effects including drowsiness, they also lack specificity in the immune system leading to global immuno-suppression. Also many of these therapeutic agents need to be administered continuously. Therefore, new improved treatments are constantly being sought to control the allergic response prophylactically and/or therapeutically without the above-mentioned limitations.
Individuals who wish to become desensitized against an allergen often must submit himself/herself to injections of measured doses of the allergen, first administered at weekly or biweekly intervals, then gradually decreases to bimonthly or monthly intervals throughout the year. Such injections generally commence with a small dose of the allergen and then gradually increasing the dosage until a maximally-tolerated maintenance dose is achieved. The individual is then kept on a maintenance dose of the allergen for long periods of time or until the individual no longer exhibits an allergic reaction to the allergen.
Other treatment regimes have been devised to reduce or eliminate an allergic response.
Allergen injection therapy (allergen immunotherapy also known as subcutaneous immunotherapy (SCIT) is known to reduce the severity of allergic rhinitis. This treatment is theorized to involve the production of a different form of antibody, a protective antibody which is termed a “blocking antibody” (Cooke, R A et al., Serologic Evidence of Immunity with Coexisting Sensitization in a Type of Human Allergy, Exp. Med. 1935; 62:733). Chemical agents have been developed which inhibit the interactions between the IgE and its receptor (Cheng et al., U.S. Pat. No. 5,965,605 and Ra et al., U.S. Pat. No. 6,090,034). IgE antagonists have also been used to treat allergic disease (Presta et al., U.S. Pat. No. 5,965,709) and compounds that exhibit immunosuppressive activity and inhibits the release of histamine (Bycroft et al., U.S. Pat. No. 5,969,158). St. Remy et al., U.S. Pat. No. 4,740,371, discloses an immune complex of an allergen for treating allergies involving a combination of the specific allergen and the corresponding antibody to that allergen. The injection of the complex into a patient is said to reduce a patient's allergic reaction to that specific allergen. Others have suggested that certain human proteins can neutralize IgE by blocking it from interacting with the mast cells, but this has not been established clearly as a clinically effective therapy (Stanworth, et al., Allergy Treatment with a Peptide Vaccine, Lancet 1990; 336:1279-81). Patterson et al., U.S. Pat. No. 5,314,690 disclosed a method and preparations for reducing IgE antibodies to allergens in allergic subjects wherein substance P (a neuropeptide) and an allergen or fragments of allergens or haptens acting as allergens are administered together to the allergic subjects through a non-oral route.
Cholera Toxin and B Subunit as Adjuvants Cholera toxin (CT) and the closely related heat-labile toxin (LT) from Escherichia coli are known as exceptionally potent immunoadjuvants when co-administered with antigens by various mucosal routes (Elson et al., J. Immunol. 1984; 133:2892-2897; Hohngren et al., Vaccin 1973; 1 1: 1179-1184; Lycke et al, Eur. J. Immunol. 1992; 22:2277-2281. Both CT and LT are recognized as “AB” toxins in that they are composed of two distinct structural and functional components: a single toxic-active A subunit component and a non-toxic cell-binding B subunit. The latter is a homopentamer component and a non-toxic affinity for GMI ganglioside receptors (Holingren et al., Nature 1981; 292:413-417). Such receptors are known to be present on most mammalian cells, e.g., on skin and other epithelial cells, on all known antigen-presenting cells including dendritic cells (DC) and Langerhan's cells (LC), as well as on B and T lymphocytes. Recently, Gleim et al., U.S. Pat. No. 5,980,898 disclosed a system for transcutaneous immunization that induces an immune response (e.g., humoral and/or cellular effectors) in an animal or human. The system provides a simple application to intact skin of both rodents and humans of a formulation comprised of antigen and an adjuvant that was whole cholera toxin.
Common to allergies is the involvement of the IgE class of antibody. Individuals are not born with allergies; rather they acquire them by exposure to allergens. The steps of the IgE allergic reaction are sensitization upon first exposure to the allergen, and then the allergic response to subsequent exposures. The allergic response consists of an immediate and delayed response referred to as the early and late phase responses respectively. In atopic individuals, those prone to allergies, the initial exposure to an antigen results in the production of IgE antibodies that specifically recognize that allergen. This process is called sensitization.
The early phase response (ERP) is the immediate reaction that occurs within minutes of exposure to an allergen. IgE are bound to the surface of a neuroimmune cell called the mast cell (in the circulation these cells are called basophils). Sufficient numbers of bound IgE antibodies that react with an allergen causes the mast cell to release its content of secretory vesicles, a process known as degranulation. The secretory vesicles contain histamine and other stored substances such as nerve growth factor (NGF). In addition the mast cell and T cells immediately begin manufacturing leukotrienes, cytokines, enzymes and substances that activate blood platelets and attract secondary cells such as eosinophils. Symptoms vary depending on the site, but common reactions are smooth muscle contraction, mucus secretion, vascular permeability, and sensory nerve stimulation.
The late phase response (LPR) develops over hours to days of exposure as eosinophils and other cells are attracted to the area. Eosinophils produce major basic protein, eosinophil cationic protein, leukotrienes and nerve growth factor. TH2 lymphocytes release cytokines that promote further IgE production and eosinophil chemo attraction, and increased numbers of mast cells.
Nerve Involvement in Allergy
The sensory nerve stimulation causes reflexes that are designed to aid in defending the tissue. These reflexes are often a larger problem then the local allergic response. Reflexes can range from large gross motor actions to regional afferent and efferent arcs or even local axon-axonal reflexes involving a single neuron.
Some reflexes recruit major motor actions that are well recognized. In the nose, sneezing is a reflex attempt to expel unwanted material and coughing is the equivalent response in the lungs.
Regional reflex arcs involve the sensing of the stimulus by the sensory neuron, the transfer of the message to the ganglia and the central nervous system and an efferent response via autonomic neurons. Reflex excitation by the autonomic nervous system directly causes mast cell to degranulate, thereby spreading the reaction. In addition these reflexes control a variety of other functions. In the nose these reflexes cause increased mucus production, increased cilia movement, nasal congestion and sneezing. In the lungs reflexes cause bronchospasm, increased mucosal congestion, production of airway secretions and coughing. In the GI tract reflexes cause dysmotility, mucosal congestion and secretions. In the skin the reflexes cause swelling and itching.
Finally there are local axon-axonal reflexes in sensory nociceptive nerve fibers. Allergic stimulation of a single neuron causes release of mediators from other axons of the same neuron. (Barnes P et al. 1991 Neuropeptides in the respiratory tract. Am Rev Rasp Dis 144:1187-1198, 1391-1399)
In chronic allergic stimulation the mast cells and eosinophils releases nerve growth factor which causes growth of the nerves in the region. Thereby allowing for increased neural responses and hyper reactivity. This hyper reactivity is not limited to allergic reactions but extends to non-allergic conditions such as respiratory tract infections including viral and bacterial infections. Specifically viral rhinitis, viral and bacterial sinusitis, suppurative otitis media, bronchitis and pneumonia. Therefore individuals become more susceptible to these conditions and have more frequent and severe infections.
Furthermore the repeated allergic reactions cause changes in the qualitative response of the neural reflexes such that they are inappropriately activated. This negatively effects non-allergic conditions, such as bronchospasm mucus production and coughing in non-allergic lung conditions such as bronchitis and emphysema.
Allergic Reactions Differ from Inflammatory Reactions
Allergic reactions differ from inflammation. Allergies represent the body's inappropriate response to what is in essence a harmless antigen. It is believed that the IgE allergic reactions evolved to combat parasitic infections which are now rare in industrialized societies. In contrast, inflammation is the body's response to actual tissue damage or infection. Inflammation is clinically distinguished by the classical symptoms of calor, rubor and dolor: heat, redness and pain. Inflammation is a process that triggers a cascade of mediators with wide effects, both locally and systemically. Local reactions include pain, vasodilation and migration of macrophages and neutrophils. Systemic reactions include fever. Certain conditions, such as rhinitis or asthma, can be triggered by allergies, infections, irritating chemicals or may be entirely neurogenic, the result of nerve activity without prior inflammatory or allergic stimulation.
Specific Allergic Conditions
Rhinitis
Allergic Rhinitis
The inner lining of the nose is a mucosa that contains serous and mucus glands and large numbers of mast cells. This mucosa extends to the openings leading to the sinuses as well as the Eustachian tube where it is continuous with the mucosa of the sinuses and middle ear, respectively. The EPR of the nasal mucosa causes mast cell degranulation. The release of histamine, heparin and neuropeptides provokes vasodilation and acute swelling of the mucosa and has some minor direct stimulatory effect on the mucus secreting glands. Reflex excitation causes reflex sneezing, congestion and neural stimulation of the seromucinous glands and further congestion. LPR attracts eosinophils and prolongs the reaction.
Allergic reactions can also be chronic, a condition known as perennial rhinitis. In these cases airborne allergens are constantly in the environment. Chronic low-level allergic reactions cause a thickening of the nasal mucosa due to edema and hypertrophy of glandular elements. As a result the primary symptoms of perennial rhinitis are nasal congestion, and postnasal drip. After each allergic reaction the mucosa swells; repeated allergic reactions enlarges the mucosa permanently and may form polyps. Thickening of the mucosa can cause obstruction of the small openings that allow drainage from the sinus. Obstruction of these openings allows nasal secretions to collect and become infected, thereby causing sinusitis.
Topical treatment of allergic rhinitis includes steroid sprays and chromalyn sodium (Nasocrom®) a chemical that blocks mast cell degranulation, and/or nasal decongestants (Neosynephrine). Systemic treatment includes oral anti-histamines and non-sedating antihistamines (Allegra®, Zyrtec®, Claritin®). Long-term therapy requires immune desensitization to the allergen by progressive intradermal injections of the allergen over months to years.
Allergic rhinitis can lead to pulmonary disease, including but not limited to asthma and emphysema, suitably asthma caused by hyperreactivity and/or the symptoms of bronchoconstriction, mucosal edema, increased secretions and cough. These can be treated by the application of CnT to the nasal cavity of patients with allergic rhinitis. It is well known in the art that allergic conditions of the nose can cause reflex changes in the lung that mimic or exacerbate asthma. (McCusker C et al 2002, Site-specific sensitization in a murine model of allergic rhinitis: Role of the upper airway in lower airway disease, J Allergy Clin Immunol, 110:891-898)
Perennial Allergic Rhinitis
Perenial rhinitis is a chronic condition and certain symptoms, such as nasal congestion, are more prominent then others such as sneezing. Therefore therapy for this condition needs to be over more prolonged period, if not indefinitely. Although the same treatments as disclosed for seasonal allergic rhinitis can be used repeatedly, certain methods of treatment are disclosed here that are more efficient and convenient for longer term therapy.
Parasympathetic neurons do not extend from the central nervous system to their target organs in the nose. Instead parasympathetic preganglionic neurons have their cell bodies in the brain stem and have an axon that extends partway and synapses on the cell body of a second neuron called the postganglionic neuron. The axons of the postganglionic neurons extend into nose and sinuses and modulate many of the biological responses seen during allergic reactions. The cell body of the post ganglionic parasympathetic neuron also receives collateral afferent synapses from sensory neurons that are stimulated during allergic reactions. Therefore much of the neuronal circuit involved in the allergic reaction converges onto the cell body of the postganglionic neuron.
All of the postganglionic neuron cell bodies are concentrated in small structure called the sphenopalatine ganglion. Moreover all afferent synaptic connections on these neurons is cholinergic, the neurotransmitter most sensitive to BoNT. Therefore application of CnT to the sphenopalatine ganglion is the most efficient way of blocking the allergic neural reaction.
The sphenopalatine ganglion is accessible to needle injection via the sphenopalatine canal. This canal passes though the hard palate and is accessible about one centimeter medial to the second molar. Injections of anesthetic and vasoconstrictor agents are commonly performed by clinicians skilled in the art of nasal surgery.
Infectious Rhinitis
Although they share some of the same symptoms, allergic rhinitis differs from infectious rhinitis. The most common cause of infectious rhinitis is a viral infection, known as the common cold. Bacterial and fungal infections of the nose occur also but these are comparatively rare as primary events. During viral infections the epithelial cells release secretions that trigger an inflammatory response. The classic signs of caldor, rubor and dolor; heat, redness, and pain characterize inflammation. White blood cells such as macrophages and neutrophils migrate from small blood vessels in the area to the infected mucosa. These cells in turn release a variety of chemical mediators that increase the inflammation. Infectious rhinitis is characterized by a purulent or pus like postnasal drip, and nasal congestion. In many viral infections there are systemic symptoms such as fever. Treatment of viral infectious is infections there are systemic symptoms such as fever. Treatment of viral infections is drugs.
Vasomotor and Other Causes of Rhinitis
Vasomotor rhinitis is strictly a neural hyper stimulation of the serous secretory glands of the nose. This condition is characterized by a watery nasal discharge with a very small content of mucus. Vasomotor rhinitis results directly from neural stimulation of temperature changes or while eating, and associated other symptoms such as congestion, and sneezing are not prominent. U.S. Pat. No. 5,766,605 discloses a method of blocking the symptom of rhinorrhea in vasomotor rhinitis using clostridia neurotoxins.
Serous Otitis Media
Direct reaction of the middle ear mucosa to allergens, or indirect effects by blockage of the Eustachian tube, leads to serous otitis media. In this condition the middle ear fills with fluid and hearing is impaired. As this condition most often affects young children, they are at risk of leaning disabilities due to the decreased hearing acuity.
Sinusitis, a Complication of Rhinitis
Sinusitis is an infection of the sinuses. The sinuses are air filled cavities surrounding and opening into the nasal cavity via small openings called ostia. The maxillary sinuses compose the mass of the cheeks and the ostia are between the inferior and middle turbinate. The frontal sinuses are above the brow underneath the skin of the forehead, they open into the nasal cavity via a duct that enters beneath the middle turbinate. The sphenoid sinuses are in the nasopharynx and have ostia on their anterior surface. The ethmoid sinuses are located between the eyes and are composed of numerous small air cells. The anterior and posterior cells drain independently. The anterior ethmoid region is especially important due to the confluence of drainage ostia. The area is called the infundibulum, and a small amount of obstruction can cause widespread sinus infections.
Sinus infections are either acute or chronic. In acute sinusitis a bacterial infection follows a viral infection of the upper respiratory tract. However, sinusitis can also occur from obstruction of the draining ostia of the sinuses by inflammation or mass lesion. Topical nasal decongestants and systemic antibiotics are used to treat acute sinusitis. Severe or complicated infections may require surgical drainage of the involved sinus. Chronic sinusitis is a low-grade ongoing or recurrent infection of the sinuses. In these cases the mucosa of the sinuses has become thickened and enlarged due to edema and increased secretory glandular elements. In these cases small abscess may persist and relatively mild inflammatory stimuli may cause obstruction of the narrowed sinus ostia. Treatment of chronic sinusitis includes topical steroid sprays, systemic anti histamines and decongestants, and/or surgical removal of diseased mucosa with enlargement of the ostia.
Asthma
Asthma is a general term given to a similar constellation of symptoms: bronchospasm, mucosal swelling and increased secretions. Allergic stimulation, infections, irritating chemicals, cold air or exercise can trigger asthma.
Allergic asthma is a specific subset of asthma that is initiated by allergens and involves the IgE mediated reaction. Local and organ reactions include bronchial smooth muscle constriction, mucosal swelling and increased secretions.
Other Allergic Conditions
Other allergic conditions include food allergies, and allergic dermatitis.
Clostridia Neurotoxins (CnT)
Clostridium (C.) botulinum and the closely related species C. butyricum and beratti produce an extremely powerful neurotoxin that causes the paralytic condition known as botulism. The botulinum neurotoxin (BoNT) protein consists of a light and heavy chain that together weigh approximately 150 kD. In botulism the primary target is the synapse of the motor neuron with the muscle fiber. Here BoNT is taken up by the membrane of the motor neuron and is internalized. The effect of BoNT is to inhibit the release of neurotransmitters and neuropeptides by neurons. In clinical use each serotype appears to differ in its potency in blocking different classes of neurons.
BoNT works by a two-stage mechanism, uptake and molecular action. Peripheral nerve terminals take up BoNT. After translocation across the cell membrane BoNT interferes with the molecular mechanism of neurosecretion. Specifically, BoNT cleaves the proteins involved in synaptic vesicle docking and release called the SNARE complex. The result is to block neural signals.
C. tetani produce tetanus neurotoxin (TeNT). TeNT is similar to the BoNTs in that it interferes with vesicle release by cleaving VAMP, one of the SNARE family of proteins. However the in vivo biological activity of TeNT is usually quite different from BoNT. The systemic disorder tetanus results from TeNT produced at a wound site and disseminated throughout the body via the blood stream. The TeNT is taken up by peripheral motor neurons and transported to the central nervous system. The TeNT then preferentially blocks inhibitory neurons connecting to the motor neuron, thereby allowing unopposed excitatory input. However, at higher doses TeNT and when introduced directly into the neuron also blocks all neurons in the same manner as BoNT. In this application it is assumed that when BoNT is discussed, it includes the TeNT when used at higher blocking doses.
At present seven immunologically distinct serotypes of the BoNT are known, named A, B, C, D, E, F and G. The type C serotype is now known to be divided into three different toxins with distinct biological effects. Only C1 is a neurotoxin, whereas C2 and C3 are not. C2 is distinctive for blocking actin formation, which can prevent mast cell degranulation. Although all BoNT serotypes interfere with proteins that cause the release of synaptic vesicles from cells they each interfere with different proteins, or different parts of the same protein:
BoNT A & E cleave SNAP-25 (synapse associated protein)
BoNT C cleaves SNAP-25 and syntaxin
BoNT B, D, F & G (and TeNT) cleave VAMP (vesicle associated membrane protein)
Most if not all cell types use the vesicle system for secretion, although the molecules within these vesicles differ for each type of cell. If experimentally introduced into any cell BoNT appears capable of blocking its vesicle release. However, in nature BoNT appears to be internalized into neurons, particularly the efferent neurons. The vesicles within neurons contain classical neurotransmitters (acetylcholine, epinephrine, nor epinephrine, dopamine, serotonin, glutamate, GABA and others) and/or neuropeptides (substance P, neurokinin A, calcitonin gene related peptide (CGRP), neuropeptide Y, interleukins, growth factors and others). Although the highest affinity of BoNT is for cholinergic neurons, in various preparations BoNT has been shown to block secretion of all these molecules.
The Clinical Effects of Botulinum Toxin on Different Classes of Neurons
Voluntary Motor Nerves
The first and still primary use of BoNT is to block motor nerve communication with muscle fibers. BoNT is injected within the target muscle. The BoNT is then internalized into motor neurons where it decreases or stops the release of the neurotransmitter acetylcholine (AChE), thereby causing paresis or paralysis of the muscle. Scott introduced the concept of localized muscular injections of BoNT in the specific condition of strabismus (squint, crossed eyes). Later BoNT was found to be particularly useful for movement disorders such as tics, spasms, contractures, cramps and tremors. More recently, the injection of BoNT into facial muscles has been found to ameliorate skin wrinkling and lines related to aging. Another recent application of BoNT injections is to decrease the pain accompanying muscle tension in conditions such as headache and temporo-mandibular joint syndrome.
Autonomic Motor Neurons
Effector neurons of the autonomic system innervate and control the contraction of smooth muscles using AChE as the neurotransmitter. Injections of BoNT have been used to decrease tone in the smooth muscles of the lower esophageal sphincter, esophagus, stomach wall, and pyloric sphincter, sphincter of Odi, anal sphincter, and urinary bladder.
Autonomic Secretory Neurons
Effector neurons of the autonomic system control or modulate the secretion of various water and mucoid fluids throughout the body. BoNT injections have been used to decrease sweating, salivary gland flow, gastric secretions including acid production, nasal and other respiratory secretions, and tearing.
Sensory Neurons
Sensory neurons release a wide variety of neuropeptides, cytokines, growth factors and other substances that effect parenchymal cells, blood vessels and immune cells. Notable is that these substances can activate mast cells directly thereby extending the allergic reaction. Except for nitrous oxide these substances are released via the SNARE mechanism and can be blocked by CnT.